Among the variety of methods known in the art of oil and water well rehabilitation and maintenance, are methods which involve the use of chemical or explosive materials for the removal of hard deposits and other encrustations. Alternative methods known in the art employ high pressure jetting techniques in the well-cleaning process. Variations of these methods are also utilized for the cleaning and maintenance of other liquid or dry storage and transport facilities such as reservoirs, crucibles, tanks, pipelines and channels.
A consideration of cleaning processes which employ explosives for the removal of hard deposits and encrustations, raises a number of important concerns. Such concerns include safety issues surrounding the manufacture, transport, usage and storage of explosive material, as well as concerns regarding the risk of structural damage to a water or oil well, or other storage or transport facility undergoing treatment.
Turning now to cleaning methods involving the use of high pressure jetting--which by way of example, are employed to remove hard scale deposits from wells and pipelines--these methods involve the application of a high pressure jet, such as a water jet, to an area of deposits, so as to first penetrate and then "strip off" the deposits by driving a fluid wedge between them and the surface to which they are attached. Disadvantages surrounding this method include limited effectiveness owing to dissipation of hydraulic power which may result from line losses, activation of the jet in a liquid environment, and difficulties in controlling movement of the jet
In addition to the above-described rehabilitation, cleaning and maintenance techniques, there are also known in the art, treatment methods which involve the use of air or gas blasting apparatus. U.S. Pat. No. 5,579,845 to Janson et al for example, entitled "Method for Improved Water Well Production", teaches generally, a method by which pressure waveforms and mass displacement within a well bore volume are used for stimulating, refurbishing or otherwise increasing production from water wells.
Referring now to U.S. Pat. No. 4,966,326, entitled "Air-Blasting Cartridge", there is described an example of air blasting apparatus which may be used for performing such treatment methods. This patent describes an air-blasting cartridge comprising a housing subdivided into an inlet chamber and a discharge chamber by virtue of a piston arranged lengthwise along a longitudinal axis of the housing. The inlet chamber communicates with a source of compressed air through an air admission tube which runs the length of the cartridge through an axial port of the piston. The discharge chamber communicates with the inlet chamber through an annular gap between the air admission tube and the piston, and is adapted to communicate with the surrounding atmosphere at the instant of its discharge, by means of at least one open-ended passage made in the housing close to the inlet chamber, wherein a pressure relief valve is provided at the outlet end of the passage.
While the above apparatus is intended for use in cleaning industrial pipelines including sewer pipelines, its efficiency especially with respect to well rehabilitation and maintenance--is limited by the very construction of the cartridge. In particular, the provision for the cartridge to communicate with the surrounding environment through the above-described pressure relief valve, creates a significant limitation upon the piston's opening speed which increases in accordance with the hydrostatic pressure. Further, the cartridge's pressure relief valves are likely to become clogged rather quickly, especially when the apparatus is used in a liquid environment containing an appreciable quantity of suspended particles.